This Small Business Innovation Research Phase II project aims to develop new targeted fluorogenic substrates capable of measuring lysosomal enzyme activity in living cells and tissues. If successful, the proposed research will provide breakthroughs needed to advance the discovery of promising new therapies and modulating drugs for lysosomal storage diseases and allied medical applications. In Phase I of this project, Marker Gene Technologies, Inc. established the feasibility of the technology by preparing new fluorogenic glycosidase, esterase, phosphatase, lipase and sulfatase substrates for lysosomal enzymes and demonstrated differential staining in living cells that were from normal or were of disease origin or upon induction of inhibition of lysosomal enzyme activities. In Phase II, these and additional new substrates will be assayed in vitro for their ability to measure specific and localized inhibition or induction of lysosomal enzymes in living cells as well as differentiate individual enzyme activities in a cell- or tissue-specific manner. These new systems will be validated for use in high-throughput screening for drug discovery, for use in clinical diagnostics to evaluate the occurrence and progression of disease, and for use in monitoring the effectiveness of existing or emerging therapeutic interventions for these disorders. The new substrates and the resulting detection systems will also provide innovative methods to quantitate lysosomal enzyme function and to screen for the influence of secondary drug or protein administration, making them useful medical research tools for a variety of significant biochemical and medical applications. The company has engaged the collaboration of several noted research laboratories and institutions as well as major pharmaceutical companies in this arena, who are eager to test the methods and systems in their existing clinical applications. The resulting assays and products will be marketed to the research, pharmaceutical, biotechnology and diagnostic industries.